Industries such as foundaries, automotive plants and any other industry in which metal castings and other parts are machined create enormous quantities of scrap material. For example, the machining of engine blocks, which are essentially cast iron, will result in a significant percentage of the engine block weight being machined off in the form of cast iron borings which are very fine metallic particles. The machining of steel parts likewise will result in steel chips and turnings which, although somewhat larger than the cast iron borings, are still relatively small.
During the machining operations, various cutting fluids will normally be used. These fluids may range from straight hydrocarbon or oil type cutting fluids to water base cutting fluids with water soluble oils therein. In a typical situation, the borings and turnings will include, by weight, from 2 to 6 percent of the cutting oil.
Recovery of the scrap borings, turnings and chips is desirable in view of the cost of basic materials. Nevertheless, recovery of these materials is expensive and difficult due to the nature of the borings and turnings. The loose nature of the borings and turnings makes them extremely difficult to handle. Additionally, it is inefficient to directly deposit the borings and turnings in a furnace or cupola inasmuch as they will float in the slag of an induction furnace or blow out the stack of a cupola and very little actual metal recovery will occur. Further, the high moisture and hydrocarbon content in the material creates a dangerous situation of moisture expansion or explosion within the furnace and also the hydrocarbon will create contamination and excessive smoking. Accordingly, direct introduction of the material is, for all practical purposes, nearly impossible.
The scrap recovery industry is currently utilizing large briquetting presses for compacting the borings and turnings into briquettes. In this operation, the material is fed cold to a briquetting press which will produce a compressed briquette ranging from a few pounds to more than 125 pounds per briquette. These cold briquettes, while a substantial improvement over the unprocessed material, do nonetheless have considerable problems. Cold briquetting does not remove the moisture or other hydrocarbons except to the extent that they are squeezed from the material during compression into a briquette. Nonetheless, there is still a considerably high percentage of moisture and hydrocarbon remaining in the finished cold briquette.
This moisture and hydrocarbon content of the cold briquette still presents considerable problems as respects the introduction of the briquette into furnaces or cupolas. The briquettes are somewhat successfully used in cupolas but they have not been successfully used in induction furnaces due to the danger of explosion within the rather narrow confines of the induction furnace. Additionally, the density of the briquette is not sufficiently high to prevent floating of the briquettes, to some degree in the molten bath. Accordingly, there is a significant weight loss of the material in the furnace by reason of entrainment in the slag and loss in the furnace gases. Additionally, the hydrocarbons present within the cold briquette cause considerable smoking and other contamination within the furnace.
The cold briquettes also suffer a severe problem of structural integrity. Notwithstanding the enormous pressures utilized in forming the briquette, the moisture and oil within the briquette as well as the fact that it was compressed cold tend to prevent the compressed particles from strongly adhering to one another. The structural integrity of the briquette is of greatest concern in transporting of the material. Very often the scrap material is collected by a scrap dealer who will transport the material to his base of operation at which the material is briquetted. The briquettes then are returned by means of truck or the like to the plant where they are to be remelted. This means that the briquettes must be loaded at the dealer's plant, transported by means of truck or the like and then ultimately unloaded and fed to the cupola or furnace. During these operations, a very substantial portion of the briquettes break up or crumble back to the loose borings and chips. This is especially true of cast iron borings which have been briquetted. The end result of this is that a substantial portion of the material cannot be used in the melting facility and must then be returned back to the dealer for rebriquetting. The effect of this is duplication of hauling expenses all of which distracts from the value of the briquette.
Various attempts have been made in the industry to overcome the foregoing problems by removing the moisture and hydrocarbons from the material prior to briquetting. Washers and dryers have been attempted. The washers will basically dissolve the hydrocarbon leaving the chips somewhat free of the hydrocarbons but still heavy with moisture. The wet material is then dried. The dryers heretofore used are essentially of the type which do not attempt to control the atmosphere within the dryer and use indirect heat or direct flames upon the material. In either case, the presence of oxygen in the dryer in conjunction with the elevated temperatures of the dryer results in oxidation of the material. Additionally, there is substantial carbon and silicon loss in the heated material. The dired material is briquetted in the normal fashion. However, the loss of carbon and silicon in the material and the presence of iron oxide seriously distracts from the value of the resultant briquette.
The washer and dryer combinations heretofore known also suffer from the problem of excessive smoke generation or pollution. The hydrocarbons, to the extent that they are not burned in the dryer, are permitted to escape to the atmosphere which creates serious problems of industrial pollution which is of great consequence in current times.